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Source: Massey University

PhD student Jacques de Satgé and Associate Professor Weihong Ji.

Mangrove forests in New Zealand are rapidly expanding.

The banded rail are declining due to predators and habitat changes.

A Massey University PhD student has been invited to be a part of a three-month secondment at the Office of the Prime Minister’s Chief Science Advisor with the hopes his research can inform holistic policy around mangrove management.

Jacques de Satgé currently studies conservation biology at Massey’s Albany campus, focusing on mangrove ecosystems in New Zealand and their importance to native birds.

Contrary to global trends, mangrove forests in New Zealand are rapidly expanding due to increased sediment and nutrients in estuaries. Mangroves help protect coastlines from erosion, act as a food source and habitat for fish, reptiles, birds, benthic fauna (organisms found on and in the seabed) and terrestrial invertebrates (animals that lack a backbone). They can trap both sediments and contaminants such as heavy metals, and are excellent at capturing and storing carbon dioxide.

However, mangrove expansion in New Zealand has the potential to replace other valuable coastal habitats such as saltmarsh and seagrass and has changed the appearance of several North Island estuaries in recent decades. These changes often drive communities to remove mangroves or limit their further spread; practices which have drawn both socio-political and academic attention in recent years.

Following a nation-wide call for expressions of interest from Chief Science Advisor Dr Juliet Gerrard, Mr de Satgé pitched his project ‘Evidence-based management of New Zealand’s mangrove forests – a bird’s eye view’ and was awarded the chance to work with various stakeholders from the Department of Conservation, regional councils, and scientific advisors to further his research.

He says he has always been interested in questions ecological in nature, and subject to socio-political scrutiny ­– questions that bring about meaningful science and contribute to a conversation the public is interested in.

“Mangroves in New Zealand represent a perfect example – they are vastly understudied, yet most people will have an opinion on them. Birds in mangroves are one part of the puzzle piece we don’t know much about, so it seemed an obvious fit to pursue the research project.”

Mr de Satgé has been in New Zealand for three years and to date his work has explored how the banded rail –a cryptic and declining native bird – makes use of mangrove forests in the estuaries in the North Island. This research is supervised by Associate Professor Weihong Ji, Dr Aaron Harmer, and Dr David Aguirre from Massey’s School of Natural and Computational Sciences.

He is part of Dr Ji’s Human-Wildlife Conflict Research Group, and his previous work has been similarly themed. His master’s thesis described the effects of urbanisation on birds across cities in Belgium, while he has previously worked on human-predator conflicts in South Africa.

“The banded rail used to be fairly widely spread across both the North and South Islands and their decline is thought to have been triggered by the introduction of predators, and changes to key habitats such as the draining of inland wetlands for agriculture,” he says.

There is little research looking at why mangroves are so important to New Zealand birds but it’s estimated 23 to 48 bird species in New Zealand make use of mangroves.

“We estimate 80 to 90 per cent of the banded rail’s population overlaps with mangrove habitat on the North Island, indicating that mangroves are likely important for the long-term survival of these birds on mainland New Zealand. My research is showing that they make extensive use of mangroves to forage and sometimes even roost in these habitats. As far as we know, banded rails don’t nest or breed in mangroves, but rather in adjacent areas of rush-saltmarsh.

“Other native birds such as the grey warbler, silvereye, fantail and shining cuckoo are known to make use of mangrove forests for breeding, foraging and roosting, while there is ample evidence that kingfishers, pukekos, white-faced herons, Australasian bitterns and welcome swallows, all make use of mangroves to some extent.”

Mr de Satgé plans to use resource-consent data to assess how mangrove forests are managed in New Zealand, what the socio-political reasons are for mangrove removal, and how birds and other fauna may be affected by current management practices.

To do this he is analysing data from regional councils whose coastlines are home to mangrove forests (Northland, Auckland, Waikato, and Bay of Plenty). His hope is to use existing data from resource consents, council monitoring programmes, and limited literature to generate a mangrove-avifauna (birds of a particular region, habitat, or geological period) report that can be fed back into councils and their policy makers, and help strengthen evidence-based decision-making in the mangrove management space.

“This has given me a unique opening to feed my research into the science-policy interface, and as a conservation biologist who firmly believes in using multi-disciplinary approaches to tackling environmental issues, I feel very lucky to have this opportunity.”